In the manufacture of semiconductor devices, a long-standing problem has been oxygen contamination. Atmospheric oxygen and water vapor still remain significant contaminants in the processing area. Oxygen readily forms unwanted oxides with the semiconductor material (e.g., silicon) to be processed and these oxides lead to imperfections in the semiconductor device. As semiconductor devices grow more complex with increasing circuit density and smaller circuit components, the effect of the oxide defects become more and more severe. The need for control over contaminating oxygen becomes critical.
Up to now a typical solution has been to flush out the process chamber to remove the ambient atmosphere from the process chamber with an inert carrier gas for a predetermined time before proceeding to the next semiconductor processing step. Of course, the problem then becomes the carrier gas purity and indeed, the purity of all process gases. These gases may then contribute unwanted oxygen to the process.
The solution to the problem of gas contamination has been to place filters or purifiers "upstream" from the process chamber to ensure the purity of source gases used in the manufacture of the semiconductor devices. Over the years various gas purification techniques based upon the principles of adsorption, absorption, chemisorption, catalytic reaction, and membrane separation have been developed to remove trace oxygen and moisture from a gas supply line. Thus the solution of flushing the ambient atmosphere from the process chamber rests upon solving the problem of gas purity.
An alternative to flushing the process chamber has been to simply remove the ambient atmosphere by low pressure (vacuum) techniques. This follows the trend in semiconductor processing toward lower process temperatures. To attain lower temperatures, control of oxides native to the processing system becomes more imperative and is generally believed to necessitate lower process pressures.
However, low pressure processing has not been completely successful and therefore pre-purified gases are often introduced into the reaction chamber to augment the effects of vacuum processing. Furthermore, lower pressures require more elaborate vacuum and pressure control equipment which add to the expense and possibilities of breakdown in the process. Processing at higher pressures (approaching ambient) is still desirable in many ways.
In addition, despite manufacturing process advances in recent years, operator error or inconsistency in the handling of semiconductor wafers, such as the loading and unloading of wafers into and out of the reactor chambers, still contributes to the oxide (moisture/oxygen) challenge regardless of the techniques used in the process chamber or the gas purification measures taken "up-stream".
To correct such errors or if the various techniques above are ineffective and the wafer is contaminated with oxides, a hydrogen purge step is performed before a particular process step is performed. Hydrogen reduces the unstable oxides formed on the wafers. However, hydrogen can be a dangerously explosive gas.
Thus, inert gas flushing, low pressure (vacuum) technology and/or the use of reducing atmospheres (hydrogen) have been only partially successful in controlling such oxides.
The present invention substantially solves or obviates many of these problems with contaminating oxygen in the processing chamber.